Using expendable metal cores for casting plastics or organic polymers



United States Patent 3,480,708 USING EXPENDABLE METAL CORES FOR CAST- ING PLASTICS OR ORGANIC POLYMERS John C. St. Clair, Box 333, RR. 2, London, Ohio 43140 No Drawing. Continuation-impart of application Ser. No. 608,506, Jan. 11, 1967. This application May 18, 1967, Ser. No. 639,299

The portion of the term of the patent subsequent to Aug. 26, 1986, has been disclaimed Int. Cl. B29c 1/14, 1/02 US. Cl. 264221 3 Claims ABSTRACT OF THE DISCLOSURE This patent is a continuation-in-part of Ser. No. 608,506, filed Jan. 11, 1967.

My disclosed method of casting plastics (or more precisely organic polymers) may be used to cast a wide variety of objects. However, the big aim of my invention is to provide a cheap method for making automobile bodies and houses out of plastics.

The most efficient method for using a plastic is to cast it. In this way the plastic may be placed, at least in theory, in the places in a cast article where the plastic will give the maximum strength to the article. For example, an inch thick sheet of solid plastic will be too weak to make a top for an automobile out of. However, two 0.375 inch thick sheets of plastic held an inch apart by bars of plastic are much stronger than the inch thick sheet of plastic even though both methods of construction contain the same Weight of plastic. The methods for predicting the strength of these highly desired hollow beams with hollow centers are very well known and accurate. These hollow beams or walls not only save plastic and give much higher strengths but also the hollow part can be filled with insulation and for houses provide a very well insulated wall. However, there has not been devised previously a cheap method for supplying the cores necessary in casting plastics for the complex and large shapes used in houses and car bodies.

'In this patent the term cast is defined as placing a liquid in a mold and having that liquid be changed into a solid that the mold and its core give a desired shape to. The liquid may be a molten plastic which on cooling forms a solid. The liquid may also be an organic liquid to which a suitable catalyst has been added. In the mold the catalyst causes the organic liquid to polymerize and form a solid. This latter method of casting is called casting polymerization.

In this patent the term core is defined as a body with solid walls placed inside a mold, when a polymer is cast, which serves the purpose of preventing the polymer from entering and being cast in certain predetermined volumes of the mold.

In this patent the term organic polymer is defined as a substance made by polymerizing or joining together organic compounds.

In this patent the term organic compound is defined "ice asmeaning a compound having a molecule in which there is at least one hydrogen attached directly to a carbon atom.

In my previous patent application Ser. No. 608,506, filed J an. 11, 1967 of which this application is a continuation-in-part I disclosed how solid cores for casting plastics could be made out of magnesium metal and after the casting process was finished the magnesium metal was dissolved out by iodine, preferably in a solution of ethyl ether. The ethyl ether and excess iodine were evaporated oiT from the magnesium iodide and the magnesium metal and the free iodine could be recovered by electrolysis of the magnesium iodide in molten form in a graphite cell. The magnesium was absorbed by a molten lead cathode. The magnesium was periodically evaporated olf. from the molten lead and the magnesium recovered for reuse. I also disclosed how that magnesium iodide could be decomposed by heating to high temperatures and the magnesium vapor separated from the iodine vapor by the dilierence of the rate of flow of the two through holes in graphite plates. This method of separation is the same in principle as that used to separate the isotopes of uranium at Oak Ridge, Tenn. However, in this case the difference between the atomic weights of iodine and magnesium is enormously greater than the difference in atomic weights of the uranium isotopes and the separation is very much cheaper.

While my preceding patent application is a big advance in the art it still requires the dissolving and the regeneration of considerable quantities of magnesium or other metals with iodine. It is also not too well adapted for casting floors where relatively thick cores are required and much metal must be dissolved if the core is made solid.

The purpose of this invention is to reduce the amount of metal that must be dissolved by from 65% to by making the metal cores hollow. In this way the cost of regenerating the metal in the cores is greatly reduced. As a result metals other than magnesium may be used as the metal for making cores with very little increase in cost. Also the solvent needed for dissolving the metal core may be practically any solvent that will dissolve the metal core without harming the plastic. There is no longer any fear that the foreign countries that have most of the iodine reserves of the world might hinder use of my method of casting plastics by charging high prices for iodine.

In this invention the metal is cast in a permanent mold the walls of which are cooled on the outside by some cooling fluid like liquid sodium mixed with liquid potassium metal. For graphite permanent molds the cooling fluid is preferably helium gas. Cooling is provided so that a layer of the metal out of which the metal core is being cast will form upon the Walls of the permanent mold. At places where it is desired to saw slits in the metal core so plastic bracing can be cast the rate of cooling of the permanent mold is increased to provide the depth of solidified metal necessary for sawing the slits. In many cases it will be possible to provide the permanent mold with protrusions on its walls so that the slits will be cast into the metal core being cast. When the casting process of the metal core is completed the metal core will be slightly heated by changing the previous cooling liquid into a heating liquid. This will very slightly melt the walls of the metal core and permit the metal core to be easily withdrawn from the permanent mold.

It is the essence of this invention that the casting of the metal core be stopped before the liquid metal in the center of the metal core solidifies. At this stage the liquid metal left in the center of the metal core is poured out. In this way the center of the metal core is made hollow which reduces the amount of metal in the core by 65% to 90%. The hollow center of the metal core permits cooling liquids to be passed through the metal core during the later casting of the plastic around the metal core. In this way very good heat control can be obtained over the casting of the plastic. Of more importance is that there will be very much less metal to dissolve out and to later recover from the solvent. Also it is of importance that the time of dissolving the metal will be very much less. This latter advantage is not only caused by there being less metal to be dissolved but also by there being a much greater area of metal exposed to the solvent in the initial interval of the dissolving of the metal core. The above greatly reduces the amount of metal that must be kept on hand in a plant using my invention to cast plastic automobile bodies or houses. It also allows solvents for dissolving out the metal core that are relatively slow.. For example acids may be used and the hydrogen produced may be removed by passing the solvent through the dissolving area so fast that the hydrogen is removed in solution in the solvent. Also solvents may be used that are required to be saturated with oxygen.

When magnesium or lead are the metals out of which the expendable metal core is cast the walls of the permanent mold are preferably made of iron. Iron is very slightly soluble in molten magnesium. To prevent the slow dissolving away of the iron permanent mold when casting magnesium metal cores the molten magnesium metal can be kept saturated with dissolved iron. It is claimed by others that chromium plating an iron mold will stop any pickup of iron from the iron mold.

When zinc or tin are the metals out of which the expendable metal core is cast the walls of the permanent mold may be made out of titanium metal. With copper, aluminum and also zinc and tin the walls of the permanent mold may be made out of impervious graphite.

After the hollow metal expendable core is made it is used in the conventional manner to cast plastics. The metal core is then dissolved out. The preferred method for dissolving out a magnesium metal core has been given. If desired hydrochloric acid may be used to react with the magnesium metal. Warm mercury may be used to dissolve out the magnesium metal. This method is very cheap but is limited by the very short supply of mercury. It should be said that the use of a magnesium expendable metal core that is dissolved out by iodine dissolved in ethyl ether is usually the preferred method for carrying out my invention.

Aluminum may be dissolved out by molten iodine either with or without another iodide present to depress the melting point of the iodine. Also iodine dissolved in an aromatic hydrocarbon may be used. The aluminum iodide is recovered by evaporating oif the excess iodine and any solvent. The aluminum iodide is reacted with metallic magnesium and the metallic aluminum is recovered. The magnesium iodide is converted to iodine and magnesium for reuse by the methods given previously.

Zinc is dissolved out by iodine in water or in a hydrocarbon solvent. The zinc iodide formed may be electrolyzed as the molten salt in a graphite cell. Or it may be reacted with oxygen at high temperatures and iodine and zinc oxide formed. The zinc oxide is reduced to metallic zinc by carbon. Zinc may also be dissolved out by a halogen acid in water. The halide of zinc formed may be converted back to zinc metal and the halogen by electrolysis. The halogen is reacted with hydrogen to form the halogen acid needed.

Copper is dissolved out by iodine in a hydrocarbon solvent. The recovery of the copper and iodine can be done by electrolysis. A very cheap method of recovery is to dissolve the copper by an ammonia solution in water which is saturated with gaseous oxygen. By distilling off the ammonia the copper is precipitated as the oxide which can be reduced by hydrogen or carbon.

Tin may be dissolved out by iodine dissolved in a chlorinated solvent such as CCl The solvent is evaporated off and the tin iodide formed may be converted back to metallic tin and free iodine by electrolysis of the molten salt in graphite cells. Or the tin iodide may be reacted with oxygen at high temperatures to form tin oxide and iodine. The tin oxide is reduced to metallic tin by carbon or hydrogen.

Lead may be dissolved out by a solution of iodine in a hydrocarbon. The solvent is evaporated off and the lead iodide is converted back to lead and iodine by electrolysis of the molten iodide in graphite cells .Or the lead iodide may be reacted with oxygen at elevated temperatures with the formation of free iodine and lead oxide. The oxide is reduced to lead by either carbon or hydrogen.

In the above only the more preferred methods for dissolving and recovering the expendable metal cores made out of various metals are given. Solvents like sulfuric acid, organic acids and in some cases nitric acid may be used to dissolve the expendable metal cores and in most cases will give forms of my invention that are superior to former methods of casting plastics.

I claim:

1. In a method for forming hollow articles having an intricate internal configuration by casting organic polymers into a mold having a metal hollow core which is dissolved out by a reaction with a solution of iodine in inert solvent after the polymer has hardened followed by solvent, metal and iodine recovery for reuse the improvement comprising forming the core by casting metal into a cooled Wall mold with the cooling stopped before the metal in the center has solidified followed by removal of the unsolidified metal center.

2. A claim according to claim 1 in which at least 20% by weight of the metal is a member selected from the group consisting of aluminum, tin, magnesium, copper, zinc and lead.

3. A claim according to claim 1 in which the metal is more than %magnesium.

References Cited UNITED STATES PATENTS 219,557 9/1879 Woodward 264-302 ROBERT F. WHITE, Primary Examiner RICHARD R. KUCIA, Assistant Examiner U.S. Cl. X.R. 

